Investigating Dose-Average Linear Energy Transfer (LETd) in Prostate Cancer Patients with Unilateral and Bilateral Metallic Hips
S Rana1*, S Pokharel1, M Kasper1, W Hsi4, (1) Lynn Cancer Institute, Boca Raton Regional Hospital, Boca Raton, FL (2) University Of Florida Proton Therapy Institute, Jacksonville, FL
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PO-GePV-T-178 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: The objective of this study was to investigate the dose-average linear energy transfer (LETd) in prostate cancer patients with unilateral and bilateral metallic hips.
Methods: Two patients with low-risk prostate cancer were selected in this retrospective study. For a unilateral hip replacement patient, the beam arrangements included a lateral proton beam combined with either posterior-oblique (LAT-PO) or anterior-oblique (LAT-AO) beams. For a bilateral hip replacement patient, we utilized three different beam arrangements:(i) two posterior-oblique beams (2PO),(ii) two anterior-oblique beams (2AO), and (iii) anterior-oblique and posterior-oblique (AO-PO). All PBS proton plans were generated for a total dose of 82Gy(RBE) with a dose/fraction of 2Gy(RBE). The mean LETd was for the CTV, rectum, and bladder.
Results: For a unilateral hip replacement patient, the mean LETd in CTV was 2.5keV/µm for both LAT-PO and LAT-AO plans. The mean LETd in the rectum was higher in LAT-AO plan (3.5keV/µm) than in LAT-PO plan (2.0keV/µm). The LAT-PO plan had a higher mean LETd in the bladder when compared to LAT-AO plan(4.7 vs. 2.3keV/µm). For a bilateral hip replacement patient, the mean LETd in the prostate varied from 2.7-2.9 keV/µm. For the rectum, the mean LETd was 2.1, 7.4, and 2.6keV/µm in 2PO, 2AO, and AO-PO plans, respectively. For the bladder, the mean LETd was 5.3, 2.9, and 3.9keV/µm in 2PO, 2AO, and AO-PO plans, respectively.
Conclusion: For both both patients, the impact of beam arrangement on the LETd in CTV was minimal. However, the selection of beam arrangement had a greater influence on the LETd distributions in the OARs, thus demonstrating a higher probability of impacting the RBE-weighted dose to the OARs when treating prostate patients with metallic hip prostheses. Beam arrangement in patients with metallic hip prostheses may be best customized to the patient anatomy and any preexisting concerns regarding specific OAR.
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